1. Field of the Invention:
This invention relates to planetary transmissions, particularly to those in which hydraulic fluid is used to brake the rotation of planet pinions to permit slippage while transferring torque between input and output means over a continuous range of input/output speed ratios.
2. Description of the Prior Art:
The prior art, exemplified by U.S. Pat. No. 2,330,375, discloses fluid braked planetary transmissions in which positive displacement gear pumps displace a fluid, the flow of which is restricted by manual or automatic valves to permit controlled slippage between input and output members. In such devices, the flow of fluid through a static restriction dissipates hydraulic energy in the form of heat, resulting in less than optimal mechanical efficiency.
Although it is known, for example in U.S. Pat. No. 3,966,367, to use planetary gears as either hydraulic pumps or motors, the applicant is not aware of any planetary transmission in which gear pumps may act simultaneously as motors to recoup pumping energy from hydraulic fluid.